Disposable personal hygiene article such as gloves, diapers and incontinence products are in widespread use. Soft, elastic films are particularly useful for personal hygiene articles and their integral components. These articles and their integral components have specific physical requirements. Ideally, these films would meet a variety of properties in addition to softness. For instance, while soft, these films would also need to have sufficient strength and an ability to withstand significant elongation. Since the articles are generally used in at least a slightly stretched condition, the films also need to retain their strength and dimension over time and at body temperature and to apply an appropriate retractive force for their particular application. Further, the films need to be stable in their environments of use and of storage, both before and after construction of the personal hygiene article.
Soft elastomeric films consisting of isoprene rubber or styrene-isoprene-styrene block copolymers are well known. One reason for their application is the inherent softness and strength of polyisoprene. Polyisoprene is, however, unsaturated and susceptible to oxidative, thermal and UV degradation. Elastomeric films for commercial application are typically melt processed at high temperatures. Unsaturated films such as made from SIS are susceptible to thermal degradation during processing. This limits the temperatures and the amount of shear that unsaturated block copolymers can experience during processing. Further, because elastomeric films used for commercial applications are stored for some time before final product manufacture and product use, long term oxidative and UV stability is important. Also, the final fabricated article will be exposed to conditions that can lead to UV, oxidative or thermal degradation. Elastomeric films fabricated from unsaturated block copolymers, while soft, present limitations in this regard. It would be advantageous to have a saturated, or hydrogenated, block copolymer which could be melt processed into soft elastomeric films. However, without formulation with other softening components, saturated block copolymers such as SEBS generally lack the combined softness and strength required for these applications.
The present invention provides an elastomeric film made from selectively hydrogenated block copolymers which has the softness of conventional SIS-based films but the stability inherent in saturated conjugated diene rubbers. We have discovered that with the proper combination of block copolymer molecular weight, monoalkenyl arene content and rubber vinyl content such soft elastomeric films can be produced and because of their selectively hydrogenated nature will be stable to thermal, oxidative and UV environments.